Known filter plates are clamped together in filter presses facing each other to form filter chambers between adjacent filter plates and have at least one flexible filter wall at least locally deformable to effectively alter the volume of the filter chamber under the operation of a pressurizing means. The filter plate has a support, the support holds the filter wall, has at least one border or frame member attached to the support, and has a pressurizable chamber for the pressurizing medium which is formed between the filter wall and the support.
To attach the frame members the juxtaposed surfaces of both pieces turned toward each other are provided with a joint, which comprises at least one engaging strip having lateral projections as seen in a cross section taken perpendicular to the face of the filter plate, and a respective joint groove for receiving the strip in the other opposing surface which is undercut. An elastic seal sealing the frame members to the support extends along the entire periphery of the frame members.
In a filter plate of the above described kind as taught in German patent DE-OS 32 20 487 the filter wall and the plate frame or frame member are formed in a single piece, which substantially determines the choice of the material for the filter wall which is limited as a rule to polypropylene. About the filter wall on a frame member the innermost strip or rib of the joint is found in the transition region between the filter wall and the frame member so that there the support is pressed tightly to the frame member.
Of course in the open filter press with the closing pressure absent, the joint has in an engaged or joined position between the support and the frame member a gap, which introduces play into the engaged or joined position, which on closing of the filter press allows a pressing together of both pieces against the resistance of the seal provided with the strip of the joint. However this free play does not extend as far as is necessary to allow the seal produced by the seal to be broken, so that in an inadvertent opening of the filter press still under filter pressure this filter pressure can be reduced quickly enough inside of the pressurized chamber. The result of this kind of operating fault can be the destruction of the filter wall and an explosive pressure reduction with all its concomitant dangers.